Dissatisfied with standard techniques for pulmonary diagnosis in children, we have evaluated the usefulness of thoracoscopy for diagnosis of intrathoracic pathology. Between July 1, 1975, and May 1, 1978, 65 thoracoscopy procedures have been performed in 57 children at the University of Florida. Thirty-four procedures were performed in immunosuppressed patients to rule out Pneumocystis carinii pneumonia. Twenty of these patients were proven to have Pneumocystis pneumonia, a diagnostic accuracy of 100%. Twelve nonimmunosuppressed patients underwent thoracoscopy for the diagnosis of persistent pulmonary infiltrates with a 100% diagnostic accuracy. Fifteen procedures were performed for the diagnosis of intrathoracic tumors. In two patients, previously unsuspected areas of involvement were encountered while in two patients false-negative biopsies were obtained. Four patients underwent therapeutic thoracoscopy. In three small infants, unsuccessful attempts were made to unroof pulmonary cysts through the thoracoscope and one patient underwent a talc poudrage. Thoracoscopy has proven to be a safe and rapid procedure which may be performed under local anesthesia without need for endotracheal intubation. In patients with pulmonary infiltrates, the accuracy has been 100%. The capability of viewing the entire hemithorax has proven valuable in evaluating children with intrathoracic tumors. Complications have included pneumothorax in six patients and bleeding in two.